This invention relates to an injection molding apparatus for manufacturing preforms for bottles, comprising a robot device having at least one robot arm, which is provided with a number of receiving tubes for reforms, the preforms in operation being disposed in the tubes such that a collar and a screw thread portion of the neck of the bottles to be formed reach outside the receiving tubes, and further comprising a mechanical pull-out device for removing preforms from the robot device, the pull-out device comprising a number of clamping elements which are positioned opposite the at least one robot arm if the robot arm is in a predetermined ejection position, while first driving means for the clamping elements are provided which can move the clamping elements towards the receiving tubes of the robot arm and away therefrom, respectively, and second driving means which can bring the clamping elements into a closed clamping position or an open position, as well as control means for the first and second driving means, the control means being arranged to bring, in a first step, the clamping elements in the open position to the receiving tubes with preforms, in a second step to close the clamping elements, and in a third step to move the closed clamping elements away from the receiving tubes again, whereby the preforms are at least partly pulled from the receiving tubes.
Preforms for bottles are conventionally manufactured in an injection molding apparatus in multiple injection molds having, for instance, 16 or 32 mold cavities. After the opening of a mold of an injection molding apparatus, the preforms are received in a robot arm brought between the mold parts, which robot arm removes the preforms from the injection molding apparatus and transfer them to, for instance, a cooling and/or discharge device. To that end, the robot arm is provided with a number of receiving tubes or receiving cavities which are arranged in a configuration corresponding to the configuration of the mold cavities. After opening of the mold, the preforms are situated on cores of the mold, and the receiving tubes or receiving cavities can be brought in front of the preforms and in line therewith, through suitable control of the robot arm. Thereafter, the preforms can be transferred to the receiving tubes of the robot arm in any of the manners known for that purpose. Thereupon the robot arm is retracted and the mold can be closed again for a next injection molding cycle.
The preforms usually comprise a smooth elongate tubular part, which is closed at one end. From this tubular part, the body of the plastic bottle to be produced is subsequently formed. The other end of the tubular part is provided with a neck portion provided with a screw thread or the like and a radial collar located between the neck portion and the smooth tubular part. The collar and the screw thread portion already have the eventual shape and size. The preforms are received in the tubes or cavities of the robot arm in such a manner that the tubular part of a preform lies in a tube or cavity with a close fit, while the collar and the screw thread portion project outside the tube or the cavity.
In addition to a retaining function, the tubes also have a cooling function.
The preforms are retained in the receiving tubes by means of vacuum. When the robot arm is located at a suitable place outside the injection molding apparatus, the preforms are removed from the receiving tubes. To that end, use can be made of compressed air, but it is also known to make use of mechanical ejection means. Thus, for instance, DE-A-42 12 115 discloses an ejection method whereby in each receiving tube of the robot arm, adjacent the closed end of the preform, a movable ejector element is arranged, by means of which the preform can be pushed out of the tube (or the cavity).
Further, from EP 0 633 119, ejection means are known that consist of strips mounted on the robot arm at the openings of the receiving tubes. The strips have openings which are in line with the receiving tubes. A preform received in a receiving tube reaches by its elongate tubular part through an opening in one of the strips into the tube located behind the opening, with the collar of the preform located in front of the preform, that is, on the side of the strip remote from the receiving tube. A strip can cooperate, for instance, with four receiving tubes, and a robot arm can be provided, for instance, with four strips. The robot arm further comprises operating means which move the strips away from the tubes, so that the preforms are pulled by their collars from the receiving tubes or receiving cavities.
An advantage of the use of mechanical ejection means is that the preforms are removed from the receiving tubes with greater certainty than is the case if exclusively compressed air is used.
A drawback of the above-described known mechanical ejection means, however, is that they are mounted on the robot arm, so that the weight of the robot arm increases. This makes the robot arm slower, which is undesired.
Another drawback is that the technique described in EP 0 633 199 is not suitable for preforms whose collar diameter is less than the diameter of the elongate tubular part of the preforms.
An injection molding apparatus of the above-described type, comprising a robot device and a mechanical pull-out device, is known from EP 0 718 084, In this known apparatus, the pull-out device is pivotally mounted on a moving carriage, while the pull-out device can pull the preforms from the cooling tubes of a robot arm and thereupon continues to retain the preforms for some time to transfer the preforms to a cooling device. The clamping elements are then clamped around the screw thread portion of the preforms. To prevent deformation of the screw thread portion, projections are used that fit accurately into the neck opening of the preforms.
The object of the invention is to obviate the drawbacks outlined and generally to provide a reliable and effective injection molding apparatus having a mechanical pull-out device for preforms. To that end, according to the invention, an injection molding apparatus comprising a robot device and a pull-out device, of the above-described type, is characterized in that the pull-out device is a stationary device, that the clamping elements are arranged, in the second step, to engage behind a collar of a preform, and that the clamping elements drop the preforms after the third step.